This invention relates to self-contained seals, particularly to devices and methods for providing a seal between two relatively rotatable machine parts, particularly suited for use in equipment for handling dry powdered material.
Manufacturing processes, such as mining and minerals, cement, or bulk powder production, require equipment that is capable of conveying, blending, mixing, or metering solids. In order to facilitate the movement of dry material through processing equipment a rotating shaft is often used, such as an agitator in the case of blending. Industries, like cement or mineral production, also force the movement of dry material that is in the form of small particles or powder by using pressurized vessels or lines. The vessels and lines used to convey raw materials must be constructed to prevent the release of particles from within a pressurized and sometimes heated system. The area around a rotating shaft is especially susceptible to the release of heated, abrasive solids. Leaks are prevented by incorporating shaft seals around the rotating shafts.
As those skilled in this art will appreciate, shaft seals for dry-material-handling equipment that operate under positive pressure can sometimes fail. Seals for this purpose typically have used high-pressure air lines to increase the pressure within seal housings. The increased pressure in the housing is higher than the pressure within the process equipment carrying the dust and solids; therefore, the dry material is unable to flow into the housing. Disadvantages of such pneumatic seals are increased cost (due to the need for maintenance and operation of air lines) and the risk of interrupted air supply. When air supply is interrupted, abrasive particles can escape from the system or into the housing of a seal. When such abrasive solids are introduced into shaft seal housing, they can quickly wear away rotating parts, leading to failure. The abrasive material will erode the vessel and surrounding parts. Therefore, the dry-material-handling industry requires shaft seals capable of preventing heated, abrasive solids under pressure from leaking without the use of pneumatic lines.